In the modern society, batteries are widely used in various apparatuses, from portable electronic products, such as a laptop computer, a camera, a mobile phone, and an MP3 player, to cars, robots, and satellites. The batteries may be classified into primary batteries and secondary batteries, and the secondary batteries are widely used due to big advantages in that the secondary batteries are repeatedly chargeable and dischargeable and that the secondary batteries are capable of storing energy.
Currently commercialized secondary batteries are nickel cadmium batteries, nickel hydrogen batteries, nickel zinc batteries, and lithium secondary batteries, and the lithium secondary batteries have the limelight due to advantages in that the lithium secondary batteries are freely charged and discharged because a memory effect is hardly generated compared to nickel-based secondary batteries, have very low self-discharge rates, and have high energy densities.
In such secondary batteries, one battery cell may be solely used, but in most cases, a plurality of battery cells are electrically connected to each other in one battery pack such that a higher output and higher capacity are obtained. In particular, recently, a smart grid system is receiving attention in terms of resolving imbalance of power supply. The smart grid system is an intelligence power grid system for increasing efficiency of using power via an interaction of power supply and power consumption by grafting an information and communication technology onto power generating, transmitting, and consuming processes. An amount of power used by a consumer may not be always uniform, but may frequently change. Representatively, an amount of power used may rapidly increase on a summer afternoon due to use of an air conditioner and may rapidly decrease at night. As such, power consumption is not uniform and may frequently change in terms of consuming power, but it is practically difficult to adapt to such power consumption even when power generation is somewhat adjusted in terms of supplying power. Accordingly, power supply surplus or power supply shortage may occur due to such imbalance between power supply and power consumption, and in this regard, the smart grid system flexibly adjusts a power supply amount by determining a power usage state in real-time. One of core components important in building such a smart grid system is a power storage apparatus. Also, such a power storage apparatus includes the much more number of battery cells that are electrically connected to each other than that of a battery pack used in a general electronic device or portable product.
A battery pack used while a plurality of battery cells are electrically connected to each other as above may be used not only in the smart grid system, but also in other various fields, such as a micro grid system and an electric vehicle charging station for supplying charging power to an electric vehicle.
As such, applied fields of the battery pack further expand to a large battery pack, and according to improvement of performance of an apparatus to which the battery pack is applied, improved performance of the battery pack itself is continuously demanded. There may be various factors for evaluating performance of the battery pack, and one of representative factors indicating the performance of the battery pack is a life.
The battery pack is an apparatus configured to be repeatedly chargeable and dischargeable, but the battery pack is no longer usable if charging and discharging cycles are repeated. In particular, performance of a secondary battery included in the battery pack may decrease as an internal material of the secondary battery deteriorates while charging and discharging are repeated, and thus a time when the battery pack does not properly operate may come.
In such a situation, the life of the battery pack should be maintained long such that the battery pack is used as long as possible. Moreover, when lives of some secondary batteries from among many secondary batteries included in the battery pack are ended, the performance of the battery pack may decrease in overall. Accordingly, the life of each secondary battery included in the battery pack needs to be lengthened as much as possible.
In particular, since a size of the power storage apparatus is very large, it is not easy to find, replace, or repair a dead secondary battery. Thus, it is preferable that the battery pack included in the power storage apparatus has a long life so as to be used for a long period of time after installation.